The present invention relates to a road antenna for use with an electric toll collection (ETC) system, which system can automatically collect a toll through radio communication without involvement of temporary stopping of a traveling vehicle which is passing through a tollgate of a turnpike.
The present invention also relates to a transmitter, a receiver, a radio system, and a method of setting a communications area, all of which are applied to narrow-band communication, such as that realized by a turnpike electric toll collection system (hereinafter referred to simply as an xe2x80x9cETC systemxe2x80x9d), and which controls an output of radio transmission established between a cell station and a mobile station.
Further, the present invention relates to a travel-speed support system which determines whether or not a vehicle is traveling in excess of a speed limit for vehicles set on a turnpike or an ordinary road and sends a notice to the driver of the vehicle when the vehicle is traveling in excess of the speed limit, as well as to an antenna for use with the system.
A traveling vehicle has conventionally been required to temporarily stop at a tollgate of a turnpike and receive a highway ticket from or pay a toll to an official, thus greatly contributing to a traffic jam. Against such a backdrop, attempts have been made to put an electronic toll collection system (ETC) into actual use as a nonstop tollgate system which eliminates a necessity for temporarily stopping a vehicle.
FIG. 27 shows an example ETC system scheduled to be put into practical use. In this drawing, a vehicle 1 is equipped with an on-vehicle radio device 2. A road antenna 4 is mounted on a post 3 and at a position above a road R. Radio communication is established between the on-vehicle radio device 2 and the road antenna 4. A vehicle sensor 5 is disposed on either side of the road R for optically detecting passage of the vehicle 1.
The antenna 4 establishes radio communication with on-vehicle radio device 2 mounted in a vehicle 1 which is passing through the post 3, to thereby specify the owner of the vehicle 1 through use of the radio device 2. For example, ID information to be used for specifying the owner of the vehicle 1 is written in the on-vehicle radio device 2.
A toll and information for specifying the owner of the vehicle 1 are written into a storage area of the antenna 4 every time the vehicle 1 passes through the post 3. The toll and the vehicle owner ID information, which have been acquired while the vehicle 1 passes through the post 3, are transmitted to an unillustrated center by way of the antenna 4. The unillustrated center summarizes tolls and on a monthly basis collects the tolls from the owner of the vehicle 1 that has passed through the post 3.
In this system, after a vehicle detector 5 disposed on the road of a turnpike has detected passage of the vehicle 1, radio communication pertaining to a toll is established between the antenna 4 and the on-vehicle radio device 2. Accordingly, collection of tolls is performed smoothly without involvement of temporary stopping of a traveling vehicle.
In terms of design of the ETC system, there is specified a coverage area of radio communication established between the on-vehicle radio device 2 and the road antenna 4. FIG. 28 is a plan view showing an example coverage area. A hatched communications area F1 is a range within which radio communication can be established between the on-vehicle radio device 2 and the road antenna 4. The remaining area; i.e., a non-response area F2, is a range in which radio communication is not permitted.
An electric field level of the road antenna 4 chiefly determines whether or not radio communication is feasible. In a case where the electric field of the road antenna 4 is greater than a predetermined level, the on-vehicle radio device 2 can perform a receiving operation, thus enabling radio communication. In contrast, in a case where the electric field of the road antenna 4 is less than a predetermined non-response level, the on-vehicle radio device 2 cannot perform a receiving operation. Accordingly, the area where the on-vehicle radio device 2 cannot establish radio communication is taken as a non-response area.
In the previously-described case, the road antenna 4 has a sharp directional pattern, and an angle at which the road antenna 4 is mounted on the post 3 greatly affects the distribution of electric field. FIG. 29 shows an example road antenna 4 mounted on the post 3. FIG. 30 shows an example distribution of receiving electric field at a position 1 meter elevated from the road R and with respect to the direction in which the vehicle travels.
As shown in FIG. 30, an electric field level L1 designates a communicable threshold level, and an electric field level L2 designates a non-response threshold level. From FIG. 30, it is understood that the communications area F1 and the non-response area F2, which are shown in FIG. 28, are embodied by reference to these threshold levels.
FIG. 31 shows an example distribution of an electric field produced in a case where only an angle xcex8 at which the road antenna 4 is mounted and is shown in FIG. 29 is changed. In this case, the predetermined communications area F1 shown in FIG. 28 is not ensured, and receiving powerxe2x80x94which is greater than the communicable threshold value level L1 and at which the on-vehicle radio device 2 can perform a receiving operationxe2x80x94exists in the non-response area F2. There is a possibility of the ETC system yielding a failure.
For example, as shown in FIG. 32, in a case where a vehicle 1A having no on-vehicle radio device and a vehicle 1B having an on-vehicle radio device passe through the ETC system while the vehicle 1B is following close behind the vehicle 1A, the vehicle sensors 5 detect the vehicle 1A. However, radio communication is established between the road antenna 4 and the on-vehicle radio device 2 of the vehicle 1B. As a result, the ETC system yields a failure, thereby permitting passage of the vehicle 1A without charge.
In order to prevent a failure, means for ascertaining in advance an angle xcex8 at which the road antenna 4 is mounted (hereinafter referred to simply as a xe2x80x9cmount anglexe2x80x9d) becomes necessary. At the time of installation of the road antenna 4, the post 3 standing at a height of 5 m or more is fixed through use of a bucket vehicle or a like vehicle. After installation of the road antenna 4, the mount angle xcex8 of the road antenna 4 cannot be readily ascertained. However, it is thought that after installation the mount angle xcex8 of the road antenna 4 may be changed by a blow or an earthquake.
FIG. 33 is a plan view showing an example coverage area. As shown in FIG. 33, in terms of design of the ETC system, there is specified a coverage area of radio communication established between the on-vehicle radio device 2 and the road antenna 4. A communications area F1 is a range within which radio communication can be established between the on-vehicle radio device 2 and the road antenna 4. The remaining area is a range in which radio communication is not permitted.
In the previous ETC system, the communications area F1 must be covered by means of the directivity of the road antenna 4. However, the transmission power of the road antenna 4 is changed for reasons of environmental or secular changes, the range of the communications area F1 is also changed, thereby resulting in a system failure. Further, depending on variation in the angle at which the road antenna 4 is mounted, the communications area F1 is greatly changed, thereby interfering with radio communication established by a vehicle which is traveling on an adjacent lane.
FIG. 34 shows a commonly-employed transmission circuit 50. In FIG. 34, reference numeral 51 designates a radio section; 52 designates a level control attenuator; and 53 designates an antenna.
The transmission circuit 50 is applied to, for example, an ETC system. According to this system, a narrow-band communications area is formed in the space between radio devices disposed on either road of a turnpike. Radio communication is established between a traveling vehicle and the road radio devices through use of a radio wave of predetermined frequency (for example, a frequency band of 5.8 GHz), to thereby collect a toll for using the turnpike.
FIG. 35 shows an antenna disposed at a tollgate of an ETC system. In FIG. 35, reference numeral 61 designates a road antenna; 62 designates an island; 63 designates a lane; and 64 designates a communications area. For example, a vehicle which is traveling in, for example, a lane 63a, establishes communication with a road antenna 61a within only a communications area 64a. 
In terms of prevention of a chance of interference arising in an radio wave used in an adjacent lane, or prevention of erroneous communication with another vehicle running before or after the vehicle of interest in the same lane, the range of communications area 64 preferably remains constant. For this reason, a transmission e.i.r.p value output from the antenna 53 shown in FIG. 34 must be set to a predetermined level.
However, variations are present in constituent elements of the transmission circuit 50; that is, the transmission output of the radio section 51 or the antenna gain of the antenna 53. In order to obviate these variations, individual constituent elements must be adjusted through use of the level control attenuator 52.
The road antenna has a directional pattern such as that shown in FIG. 36, and a communications area of the road antenna differs according to an angle at which the antenna is mounted. Consequently, the angle must be adjusted in order to ensure a desired communications area. Measurement of receiving field intensity at each angle requires a great deal of manpower.
Moreover, the ETC system must ensure highly-reliable communication. To this end, a communication area in which radio communication is to be established and a non-response area in which no radio communication is to be established must be embodied in compliance with specifications of system design. Therefore, such specifications are usually accomplished by imparting a sharp directional pattern to the road antenna.
However, the radio wave emitted from the road antenna or the on-vehicle device spreads not only to a lane of interest but also to the opposite lane, because of multiple reflections of a radio wave induced by vehicles or surrounding facilities. Therefore, radio communication is erroneously established with an oncoming vehicle to which a charge is not allowed to be charged, and a toll may be erroneously charged to an oncoming vehicle.
Further, the ETC system eliminates a necessity of temporarily stopping a vehicle at a tollgate. However, a traveling vehicle may pass through a tollgate at high speed or keep traveling at the same speed even after the vehicle has entered an ordinary road. Thus, a vehicle becomes apt to induce a traffic accident. In order to prevent a traffic accident, there is needed a travel-speed support system for measuring a travel speed of a vehicle which is traveling on a road adopting an ETC system, to thereby realize smooth travel.
In association with actual use of a turnpike ETC system, a necessity for temporarily stopping a vehicle at a tollgate is eliminated. As a result, it is predicted that a traveling vehicle passes through a tollgate at high speed or enters an ordinary road from a turnpike without being aware of a change in legal speed.
Moreover, in order to avoid establishment of radio communication with a vehicle which is traveling in an adjacent lane, the ETC system establishes radio communication at a frequency of 5.8 GHz within a narrow communications area F1 formed by the road antenna 4.
FIGS. 37A and 37B show the directional patterns of the road antenna. FIG. 37A shows a horizontal directional pattern of the road antenna 4, and FIG. 37B shows a vertical directional pattern of the road antenna 4. As is evident from these characteristic plots, the road antenna 4 shows horizontal and vertical directional patterns in which a communication area can be formed within a narrow range of xe2x88x9220 to +20 degrees relative to the center.
FIG. 38 shows an example communications area formed by a radio wave emitted from the road antenna. As indicated, the oblique line shading represents the signal strength of the radio waves. The signal is strongest in the lane of interest (6) and week or nonexistent in the adjacent lanes (6L, 6R). When a roof-like structure is present, as shown in FIG. 39, the radio wave is reflected off of a roof-like structure (11). FIG. 40 illustrates the effective mirror-image antenna (4i) position produced by the reflection of the transmission of the antenna (4) by the roof-like structure. As shown in FIG. 41, since the mirror-image antenna (4i) is located higher than the antenna (4), this results in an undesirable larger communications area which encompasses the lane of interest (6) and the adjacent lanes (6L,6R).
The present invention has been conceived to solve such a drawback of the background art and is aimed at providing a road antenna in which an angle at which the road antenna is mounted can be readily ascertained after the road antenna has been mounted on a post.
The present invention has been conceived to solve such a drawback of the background art and is aimed at providing a road antenna which can prevent occurrence of a change in a communications area by means of controlling the road antenna and prevent occurrence of a system failure or interference of radio communication established by a vehicle traveling on an adjacent lane.
The present invention has been conceived to solve such a drawback of the background art and is aimed at providing a transmitter, a receiver, a radio system, and a communications area setting method, all of which enable savings in labor required for measuring field intensity and ensure a desired communications area.
The present invention has been conceived to solve such a drawback of the background art and is aimed at providing a road antenna which prevents occurrence of erroneous communication with an oncoming vehicle traveling in the opposite lane.
The present invention is aimed at providing a travel-speed support system which sends to a vehicle which travels in excess of a speed limit a warning to reduce travel speed, to thereby prevent traveling of a vehicle at extralegal speeds and support smooth travel of a vehicle on a turnpike or an ordinary road.
The present invention has been conceived to solve the drawback of the background art and is aimed at providing a road antenna which can form a narrow communications area even when a structure is located at an elevated position above the road antenna.
According to first aspect of the invention, a road antenna comprises a road antenna which is mounted on a post and at an elevated position on a road and establishes radio communication with an on-vehicle radio device mounted in a vehicle which is traveling over the road; and a laser-beam emitting device which is mounted on the road antenna and radiates a laser beam onto a predetermined position on the surface of the road. An offset in the angle at which a road antenna is mounted can be readily ascertained on the basis of a distance between a predetermined position on the surface of the road and a position on the road surface onto which a laser beam is actually radiated.
Preferably, the road antenna according to the first aspect further comprises a laser-beam receiving device which is mounted on the predetermined location on the surface of the road and receives a laser beam emitted from the laser-beam emitting device, wherein the operation of the road antenna is stopped when the laser-beam receiving device cannot receive the laser beam. In a case where the laser-beam receiving device fails to receive a laser beam emitted from a laser-beam emitting device that has been disposed at a predetermined elevated position above the road at the time of installation of the road antenna, it becomes evident that a change has arisen in the angle at which the road antenna is mounted. Therefore, the operation of the road antenna is stopped in order to avoid an operation failure of an electric toll collection system.
According to a second aspect of the invention, a road antenna comprises:
a road antenna which is disposed at an elevated position above a road and establishes radio communication with an on-vehicle device mounted in a vehicle traveling on the road; a receiver which is disposed at a predetermined location on the surface of the road and within a communications area, receives a radio wave output from the road antenna, and outputs a signal proportional to the power of the radio wave; and a controller for determining transmission power of the road antenna on the basis of the signal output from the receiver, wherein the controller controls the road antenna so as to prevent the transmission power of the road antenna from exceeding a predetermined value. The receiver detects the transmission power of the road antenna, and a signal proportional to the thus-detected transmission power is fed back to the controller, to thereby adjust the transmission power of the road antenna so as to prevent occurrence of a change in the communications area.
Preferably, receivers are disposed at respective corners of the communications area formed on the road, and the controller determines, from signals output from the respective receivers, the angle at which the road antenna is mounted, to thereby detect an offset in the angle of the antenna with respect to a predetermined angle. The signals output from the respective receivers are fed back to the controller, and the controller detects, on the basis of these signals, the angle at which the road antenna is mounted, to thereby detect an offset from a preset initial angle of the road antenna.
According to third aspect of the invention, the present invention provides a method of setting a communications area, comprising the steps of: measuring a receiving rate for each of frames of a received signal when a receiver receives a radio wave transmitted from a transmitter; detecting change in receiving rate on a per-frame basis, the change being induced by a change in a transmission output of the radio wave transmitted from the transmitter; and setting, into the transmitter, a transmission output obtained when there is detected a receiving rate suitable for a desired communications area established between the transmitter and the receiver. The method ensures a desired communications area through simple procedures while avoiding manpower required for measuring field intensity.
According to the fourth aspect of the present invention, a radio system comprises: a transmission section including a modulation section for producing a modulation signal, gain controller for controlling a transmission output, a power amplification section for amplifying a transmission signal to a desired level, and an antenna; and a receiving section including an antenna, frequency converter for converting into an intermediate frequency a high-frequency signal received by way of the antenna, a demodulation section for demodulating the intermediate frequency, decoder for converging a demodulated signal into digital data, and receiving rate detector for detecting a receiving rate for each of frames of a received signal. On the basis of the receiving rate detected on a per-frame basis by the receiving rate detector of the receiving section, the gain controller of the transmission section varies a transmission output. As a result, a desired communications area can be set in a space between the transmission section and the receiving section. At this time, measurement of field intensity is not necessary.
The present invention according to the fifth aspect of the invention provides a transmitter comprises: a modulation section for producing a modulation signal; gain controller for controlling a transmission output; a power amplification section for amplifying a transmission signal to a desired level; and an antenna, wherein the gain controller varies the transmission output on the basis of a receiving rate for each frame determined when a receiver receives a transmission signal. On the basis of the receiving rate detected on a per-frame basis by the receiver, the transmission output of the transmitter can be set to a value at which a desired communications area can be realized.
Preferably, the gain controller comprises a data setting device and a voltage-controlled amplifier and can freely change a communication area by means of variation of an amplification gain. The communications area can be varied by means of changing the gain of the voltage-controlled amplifier.
Preferably, the gain controller comprises a data setting device and a voltage-controlled amplifier and can freely change a communication area by means of variation of an amplification gain. A communications area can be varied by means of varying the amount of attenuation of the voltage-controlled attenuator.
Preferably, the antenna has a function of adjusting the angle at which the antenna is disposed, by means of a signal output from the receiving rate detector, and can freely change a communications area by means of changing the angle. The angle at which the antenna is mounted is changed, to thereby enable changing of a communications area.
According to the sixth aspect of the invention, a receiver comprises: an antenna for receiving a radio wave transmitted from a transmitter; frequency converter for converting into an intermediate frequency a high-frequency signal received by way of the antenna; a demodulation section for demodulating the intermediate frequency; decoder for converting the demodulated signal into digital data; and receiving rate detector for detecting a receiving rate for each of frames of the received signal, wherein a communications area can be freely changed by means of changing a transmission output of the transmitter on the basis of the receiving rate for each frame detected by the receiving rate detector. On the basis of a receiving rate obtained on a per-frame basis, a transmission output of the transmitter can be set such that a desired receiving area is realized.
According to the seventh aspect of the invention, a road antenna comprises: a road antenna which is disposed at an elevated position above a road and establishes radio communication with an on-vehicle device mounted in a vehicle traveling on the road; Doppler signal processor which detects the traveling direction of the vehicle on the basis of a change arising in the frequency of a reflected wave due to the Doppler effect, the reflected wave being formed when a transmission wave emitted from the road antenna is reflected by the vehicle; and controller for inhibiting establishment of communication with a vehicle traveling in the lane opposite to the lane in which the detected vehicle is traveling. A transmission wave is transmitted from the road antenna disposed at an elevated position on the road, and the vehicle reflects the transmission wave, to thereby produce a reflected wave. The thus-reflected wave is received by the road antenna. From the reflected wave, Doppler signals which shift in proportion the speed of the vehicle are detected, and the traveling direction of the vehicle is detected by utilization of the Doppler effect. Thus, radio communication is established with only a vehicle traveling in a lane of interest, and establishment of communication with a vehicle traveling in the opposite lane is inhibited.
Preferably, the road antenna comprises reflected wave extraction means which receives the reflected wave produced when the transmission wave emitted from the road antenna for establishing radio communication and collecting a toll is reflected by the vehicle as well as a receipt wave emitted from the on-vehicle device mounted in the vehicle, to thereby extract only the reflected wave. By utilization of a reflected wave produced when a transmission wave emitted to the on-vehicle device for establishing radio communication and collecting a toll is reflected by the vehicle, the traveling direction of the traveling vehicle is detected by the Doppler effect, thereby inhibiting establishment of communication with the vehicle traveling in the opposite lane.
According to the eighth aspect of the invention, a travel-speed support system comprises: on-vehicle radio device to be mounted in a traveling vehicle; an antenna which establishes radio communication with the vehicle and is to be mounted in a position above a road; and determination means which is provided in the antenna and determines whether or not the travel speed of the vehicle is appropriate for a speed limit imposed on a road, on the basis of the travel speed of the vehicle and a signal corresponding to a reflected wave, the reflected wave being produced as a result of a radio emitted from the antenna being reflected by the vehicle when the vehicle approaches or departs from the antenna. A warning to reduce travel speed can be sent to a driver of a vehicle which is traveling in excess of a speed limit, to thereby limit the speed of a vehicle on a road interconnecting a turnpike to an ordinary road. As a result, the present invention can urge a driver to practice safe driving on a road interconnecting a turnpike and an ordinary road.
Preferably, the antenna comprises: receiver for receiving a reflected wave, the reflected wave being produced when a radio transmitted to the on-vehicle unit is reflected by the vehicle; and detector for detecting a signal received by the receiver and the speed of the vehicle. The travel speed of the vehicle can be limited on the basis of the received signal and the detected travel speed of the vehicle.
Preferably, the antenna comprises: speed warning means which compares the travel speed of the vehicle detected by the detector with a predetermined warning speed, determines whether or not the speed of the vehicle exceeds the warning speed, and issues a warning to the vehicle if the vehicle exceeds the warning speed. A warning message can be sent to the driver of a vehicle which is traveling in excess of a speed limit, on the basis of the received signal and the detected travel speed of the vehicle.
The present invention provides an antenna for use with a travel-speed support system, comprises on-vehicle radio device to be mounted in a traveling vehicle; an antenna which establishes radio communication with the on-vehicle radio device and is to be disposed at a position above a road; and measurement means for measuring the speed of the traveling vehicle on the basis of a signal corresponding to a reflected wave by means of the Doppler effect when the vehicle approaches or departs from the antenna, the reflected wave being produced when a radio wave is reflected by the vehicle, wherein the road includes both a turnpike and an ordinary road. A limit is imposed on a driver of a vehicle which is traveling in excess of a speed limit, to thereby prevent a car accident. Thus, the present invention can enable the driver to ascertain that his vehicle is traveling in excess of a speed limit and send a warning to the driver. As a result, a car traveling in excess of a speed limit imposed on a turnpike or an ordinary road can be prevented.
Preferably, the antenna comprises: receiver for receiving a wave which is reflected by the vehicle, as a result of a radio wave being transmitted to the on-vehicle radio device; and detector for detecting the signal received by the receiver and the speed of the vehicle. A limit can be imposed on the speed of a vehicle on the basis of a received signal and the detected speed of the vehicle.
Preferably, the antenna comprises: speed warning means which compares the travel speed of the vehicle as detected by the detecter with a predetermined warning speed, determines whether or not the speed of the vehicle exceeds the warning speed, and issues a warning to the vehicle if the vehicle exceeds the warning speed. A warning can be sent to a driver of a vehicle which is traveling in excess of a speed limit, on the basis of a received signal and the detected speed of the vehicle, to thereby cause the driver to ascertain that his vehicle is traveling in excess of a speed limit.
According to the ninth aspect of the invention, a road antenna comprises: a road antenna which is disposed at an elevated position on a road and sets a predetermined communications area on the road; and a roof-shaped structure which is located at an elevated position above the road antenna, the side of the structure opposite the road antenna being provided with a radio-wave absorbing material, wherein radio communication is established between the road antenna and an on-vehicle device mounted in a vehicle traveling on the road and within the communications area. Preferably, as the radio-absorbing member there may be used a sheet-like radio-wave absorbing member, a paint-like radio-wave absorbing member, or a multilayer radio-absorbing member.
A radio wave emitted from the road antenna is reflected by a road, and the thus-reflected radio wave is absorbed by the radio-wave absorbing member provided on the roof-shaped structure. As a result, there is formed a narrow communications area, which would also be formed when no structure is present above the road antenna.